The present invention relates generally to the field of organometallic compounds. In particular, the present invention relates to trialkyl Group VA metal compounds which are suitable for use as precursors for chemical vapor deposition.
Metal films may be deposited on surfaces, such as non-conductive surfaces, by a variety of means such as chemical vapor deposition (xe2x80x9cCVDxe2x80x9d), physical vapor deposition (xe2x80x9cPVDxe2x80x9d), and other epitaxial techniques such as liquid phase epitaxy (xe2x80x9cLPExe2x80x9d), molecular beam epitaxy (xe2x80x9cMBExe2x80x9d), and chemical beam epitaxy (xe2x80x9cCBExe2x80x9d). Chemical vapor deposition processes, such as metalorganic chemical vapor deposition (xe2x80x9cMOCVDxe2x80x9d), deposit a metal layer by decomposing organometallic precursor compounds at elevated temperatures, i.e. above room temperature, either at atmospheric pressure or at reduced pressures.
A wide variety of metals may be deposited using such CVD or MOCVD processes. See, for example, Stringfellow, Organometallic Vapor Phase Epitaxy: Theory and Practice, Academic Press, 2nd Edition, 1999, for an overview of such processes. Organometallic compounds of arsenic, antimony, and bismuth are used to deposit epitaxial films in the semiconductor and related electronic industries. Epitaxial films such as gallium arsenide find applications in optoelectronic devices such as detectors, solar cells, light-emitting diodes (xe2x80x9cLED""sxe2x80x9d), lasers and electronic switching devices such as field effect transistors (xe2x80x9cFET""sxe2x80x9d) and high electron mobility FET""s (xe2x80x9cHEMT""sxe2x80x9d). Ternary arsenic alloys also exist such as gallium indium arsenide (xe2x80x9cGaInAsxe2x80x9d) and aluminum indium arsenide (xe2x80x9cAlInAsxe2x80x9d), which are more attractive than GaAs or aluminum gallium arsenide (xe2x80x9cAlGaAsxe2x80x9d) for the most powerful fiber optic systems operating in the 1.3 to 1.55 micron wavelength range. Gallium arsenide phosphide (xe2x80x9cGaAsPxe2x80x9d) is suitable for visible LED""s and fiber optic emitters/detectors. Trimethylarsine in particular has been used as a precursor for carbon doping. Antimony and antimony alloy films are useful in fiber optics communication systems, particularly in the 1.3 and 1.55-micron regions. Antimony-containing semiconductor materials also have commercial applications including detection for seeker, night vision and surveillance devices (infrared detectors) and sources (LED""s or lasers). A variety of binary, ternary and quaternary Group III/V semiconductor systems containing antimony have been evaluated for applications in infrared emitters and detectors operating in the 3 to 5 micron and 8 to 12 micron spectral ranges. These wavelength ranges are important since they are natural windows in the atmosphere for infrared transmission. Epitaxial antimony-based Group III/V semiconductors have potential applications in long wavelength detectors and high-speed electronic devices.
For such semiconductor and electronic device applications, these Group VA metal alkyls must be highly pure and be substantially free of detectable levels of both metallic impurities, such as silicon and zinc, as well as oxygenated impurities. Oxygenated impurities are typically present from the solvents used to prepare such organometallic compounds, and are also present from other adventitious sources of moisture or oxygen.
The most common method of preparing Group VA metal alkyl compounds consists of reacting Group VA metal trihalides with Grignard reagents in an ethereal solvent, such as alkyl ethers, glymes or tetrahydrofuran. Aluminum alkyls can also be used instead of Grignard reagents in the preparation of Group VA metal alkyl compounds. For example, Zakharkin et al., Bull. Acad. Sci. USSR, 1959, p1853, discloses a method of producing trialkyl compounds of antimony and bismuth, as shown in equation (I), where R is ethyl, n-propyl or iso-butyl and X is chloride or fluoride.
MX3+R3Al+diethyletherxe2x86x92MR3+AlX3xe2x80x83xe2x80x83(I) 
Trace amounts of ethereal solvent invariably remain in the target organometallic compound obtained using conventional techniques. Such residual ethereal solvent contributes oxygen as a deleterious impurity in metal films deposited from such precursor compounds.
Attempts have been made to synthesize Group VA organometallics in non-ethereal solvents. For example, Takashi et al., J. Organometal. Chem., 8, pp 209-223, 1967, disclose the reaction of antimony trichloride with triethylaluminum in hexane. Such reaction was found to produce triethylstibine in extremely low yields (only about 10%), the remainder being about 42% metallic antimony and about 46% of an antimony-aluminum complex, (SbEt4)(Al2Et5Cl2). This article does not teach how to obtain triethylstibines free of antimony-aluminum complexes.
U.S. Pat. No. 4,906,762 (Sawara et al.) discloses a method of producing pure trialkylarsines from aluminum alkyls and diarsenic trioxide using alkali metal halides as complexing agents in hydrocarbon solvents. The method constitutes a two-step synthesis, both stages being heterogeneous reactions with final yields not more than 65%, and rendering highly reactive/pyrophoric reaction residues. Tertiary amines are not disclosed in this patent.
There is thus a need for methods for preparing Group VA metal alkyls in high yields with less reactive reaction residues and for Group VA metal compounds substantially free of both metallic and oxygenated impurities for use as precursor compounds for CVD.
It has been found that Group VA metal alkyls can be prepared in high yield and in high purity by reacting Group VA trihalides and Group IIIA alkyls in the presence of tertiary amines in hydrocarbon solvents. Group VA alkyl compounds produced by this method are extremely pure and substantially free of oxygenated impurities.
In one aspect, the present invention provides a method for preparing trialkyl Group VA metal compounds including the step of reacting a Group VA metal trihalide with a Group IIIA compound of the formula RnM1X3xe2x88x92n in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C1-C6)alkyl; M1 is a Group IIIA metal; X is halogen and n is an integer from 1-3.
In a second aspect, the present invention provides a method for depositing a film of a Group VA metal on a substrate including the steps of: a) conveying a Group VA metal source compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the Group VA metal source compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the Group VA metal source compound is prepared by the method including the step of reacting a Group VA metal trihalide with a Group IIIA compound of the formula RnM1X3xe2x88x92n in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C1-C6)alkyl; M1 is a Group IIIA metal; X is halogen and n is an integer from 1-3.
In a third aspect, the present invention provides a method for manufacturing an electronic device including the step of depositing a film of a Group VA metal on an electronic device substrate including the steps of: a) conveying a Group VA metal compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the Group VA metal compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the Group VA metal compound is prepared by the method including the step of reacting a Group VA metal trihalide with a trialkyl Group IIIA compound of the formula RnM1X3xe2x88x92n in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C1-C6)alkyl; M1 is a Group IIIA metal; X is halogen and n is an integer from 1-3.
In another aspect, the present invention provides trialkylantimony compounds substantially free of ethereal solvents. In still another aspect, the present invention provides trialkylbismuth compounds substantially free of ethereal solvents.
As used throughout this specification, the following abbreviations shall have the following meanings, unless the context clearly indicates otherwise: xc2x0 C.=degrees centigrade; NMR=nuclear magnetic resonance; mtorr=millitorr; g=gram; L=liter; ca.=approximately; mm=millimeters; and mL=milliliter.
xe2x80x9cHalogenxe2x80x9d refers to fluorine, chlorine, bromine and iodide and xe2x80x9chaloxe2x80x9d refers to fluoro, chloro, bromo and iodo. Likewise, xe2x80x9chalogenatedxe2x80x9d refers to fluorinated, chlorinated, brominated and iodinated. xe2x80x9cAlkylxe2x80x9d includes linear, branched and cyclic alkyl. Unless otherwise noted, all amounts are percent by weight and all ratios are molar ratios. All numerical ranges are inclusive and combinable in any order.
The present invention provides a method for preparing trialkyl Group VA metal compounds including the step of reacting a Group VA metal trihalide with a Group IIIA compound of the formula RnM1X3xe2x88x92n in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C1-C6)alkyl; M1 is a Group IIIA metal; X is halogen and n is an integer from 1-3. Preferred Group VA metals include antimony (xe2x80x9cSbxe2x80x9d), arsenic (xe2x80x9cAsxe2x80x9d) and bismuth (xe2x80x9cBixe2x80x9d). Suitable Group VA trihalides are those having the general formula MX3, where M is a Group VA metal and each X is independently fluorine, chlorine, bromine or iodine. It is preferred that X is chlorine, bromine or iodine. Group VA trichlorides are more preferred. Particularly suitable Group VA metal halides include, but are not limited to, antimony trichloride, antimony tribromide, antimony triiodide, arsenic trichloride, arsenic tribromide, arsenic triiodide, bismuth trichloride, bismuth tribromide, bismuth triiodide and mixtures thereof. It will be appreciated that mixed halide compounds may also be advantageously used in the present invention. Such Group VA metal trihalides are generally commercially available from a variety of sources or may be prepared by a variety of methods known in the literature.
A wide variety of Group IIIA compounds may be used in the present invention. Suitable Group IIIA compounds useful in the present invention typically have the formula RnM1X3xe2x88x92n, wherein each R is independently selected from (C1-C6)alkyl; M1 is a Group IIIA metal; X is halogen; and n is an integer from 1 to 3. M1 is suitably boron, aluminum, gallium, indium and thallium. Preferably, X is selected from fluorine, chlorine or bromine. Suitable alkyl groups for R include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, and the like. Preferred alkyls include, methyl, ethyl, n-propyl and iso-propyl. In one embodiment, it is preferred that n is 3. Such Group IIIA compounds where n is 3 include trialkylboron, trialkylaluminum, dialkylaluminum halide, trialkylgallium, trialkylindium and trialkylthallium, with trialkylaluminum compounds being preferred. In an alternate embodiment, it is preferred that n is 1 or 2. Such Group IIIA compounds where n is 1-2 include dialkylaluminum chlorides. Group IIIA compounds are generally commercially from a variety of sources or may be prepared by a variety of methods known in the literature.
Any tertiary amine may suitably be used in the present invention. Suitable tertiary amines include, but are not limited to, those having the general formula NR4R5R6, wherein R4, R5 and R6 are independently selected from (C1-C6)alkyl, di(C1-C6)alkylamino-substituted (C1-C6)alkyl, and phenyl and wherein R4 and R5 may be taken together along with the nitrogen to which they are attached to form a 5-7 membered heterocyclic ring. Such heterocyclic ring may be aromatic or non-aromatic. Particularly suitable tertiary amines include, but are not limited to, trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, tri-iso-propylamine, tri-iso-butylamine, dimethylaminocyclohexane, diethylaminocyclohexane, dimethylaminocyclopentane, diethylaminocyclopentane, N-methylpyrrolidine, N-ethylpyrrolidine, N-n-propylpyrrolidine, N-iso-propylpyrrolidine, N-methylpiperidine, N-ethylpiperidine, N-n-propylpiperidine, N-iso-propylpiperidine, N,Nxe2x80x2-dimethylpiperazine, N,Nxe2x80x2-diethylpiperazine, N,Nxe2x80x2-dipropylpiperazine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,2-diaminoethane, pyridine, pyrazine, pyrimidine, and mixtures thereof. Preferred amines include trimethylamine, triethylamine, tri-n-propylamine, triiso-propylamine, and tri-n-butylamine. More preferably, the tertiary amine is triethylamine or tri-n-propylamine. It will be appreciated by those skilled in the art that more than one tertiary amine may be used in the present invention. Such tertiary amines are generally commercially available from a variety of sources. Such tertiary amines may be used as is or, preferably further purified prior to use.
A wide variety of organic solvents may be used in the present invention, provided that such organic solvents do not contain oxygenated species. It is further preferred that the organic solvents do not contain oxygen. Particularly suitable organic solvents include, but are not limited to, hydrocarbons and aromatic hydrocarbons. Preferred organic solvents include benzene, toluene, xylene, pentane, hexane, heptane, octane, decane, dodecane, squalane, cyclopentane, cyclohexane, cycloheptane, and mixtures thereof. More preferably, the organic solvent is benzene, toluene, xylene, hexane, heptane, cyclopentane or cyclohexane. It will be appreciated that more than one organic solvent may be advantageously used in the present invention. In an alternative embodiment, the tertiary amine may be used as the organic solvent. Such organic solvents are generally commercially available from a variety of sources. Such solvents may be used as is or, preferably, purified prior to use.
Preferably, such organic solvents are deoxygenated prior to use. The solvents may be deoxygenated by a variety of means, such as purging with an inert gas, degassing the solvent in vacuo, or a combination thereof. Suitable inert gases include argon, nitrogen and helium, and preferably argon or nitrogen.
In the process of the present invention, Group IIIA compound, tertiary amine and organic solvent may be combined in any order prior to reacting with the Group VA metal trihalide. Preferably, the Group IIIA compound is first combined with the tertiary amine to form an amine-Group IIIA adduct. Typically, the amine-Group IIIA adduct may be formed at a wide variety of temperatures. Suitable temperatures for forming the adduct are from ambient to 90xc2x0 C. The Group VA metal trihalide is then reacted with the amine-Group IIIA adduct to form the desired trialkyl Group VA metal compound. It is preferred that the Group VA metal trihalide is added dropwise, either neat or as a hydrocarbon solution, to the amine-Group IIIA adduct. Suitable temperatures to form the trialkyl Group VA compound are from about ambient to 80xc2x0 C. A wide variety of tertiary amines and organic solvents may be used in the present invention. Thus, in a preferred embodiment, the present invention provides a method for preparing trialkyl Group VA metal compounds including the steps of reacting a Group IIIA compound with a tertiary amine to form an amine-Group IIIA adduct in an organic solvent that is free of oxygenated species; and reacting the amine-Group IIIA adduct with a Group VA metal trihalide in the organic solvent. It is further preferred that the Group IIIA compound is a trialkylaluminum or dialkylaluminum chloride.
In general, the tertiary amine is present in a stoichiometric amount to the Group IIIA compound. The amount of Group VA trihalide is, typically, in a stoichiometric amount to the Group IIIA compound, the stoichiometry being dependent on the nature of Group IIIA compound, Group VA compound, and the tertiary amine selected. The molar ratio of Group IIIA to Group VA Compound ranges from 1 to 3. It is anticipated that molar ratios greater than 3 will also be effective.
The specific tertiary amine and organic solvent used depend upon the particular trialkyl Group VA compound desired. For example, the organic solvent and tertiary amine may be selected such that they are more volatile or less volatile than the desired trialkyl Group VA compound. Such differences in volatility provide easier separation of the trialkyl Group VA compound from both the amine and organic solvent. The trialkyl Group VA compounds of the present invention may be suitably purified by distillation.
An advantage of the present invention is that trialkyl Group VA compounds prepared are substantially free of ethereal solvents, and preferably free of ethereal solvents. A further advantage is that the trialkyl Group VA compounds are substantially free of metallic impurities, preferably they are substantially free of zinc and silicon. The present trialkyl Group VA compounds are substantially free of silicon. By xe2x80x9csubstantially freexe2x80x9d it is meant that the present compounds contain less than 0.5 ppm of such impurities. For example, trimethylantimony prepared according to the present invention contains about 0.1 ppm silicon as compared to 2 ppm in conventionally prepared trimethylantimony. Trimethylarsenic prepared according to the present invention contains about 0.3 ppm silicon as compared to 3 ppm in conventionally prepared trimethylarsenic. A still further advantage is that the amount of air-sensitive reaction waste is reduced significantly as compared to conventional methods of preparation that typically generate either pyrophoric or highly toxic reaction residues. Trialkylantimony compounds prepared using conventional ethereal processes produce weak trialkyl antimony-ether complexes. Such complexes are very difficult to remove and can cause contamination in films produced from them. Such ether complexes are avoided by the present invention.
The present invention provides a trialkyl Group VA metal compound substantially free of ethereal solvents and aluminum complexes, wherein the Group VA metal compound is selected from trialkylstibine, trialkylarsine and trialkylbismuth. The present invention is particularly useful for preparing trimethyl Group VA compounds. Thus, the present invention further provides trimethyl Group VA metal compounds substantially free of ethereal solvents and aluminum complexes. Such trimethyl Group VA compounds are also substantially free of zinc and silicon. Preferred trimethyl Group VA compounds are trimethylstibine, trimethylarsine and trimethylbismuth. Thus, the present invention further provides trialkyl Group VA metal compounds that are substantially free of zinc and silicon, and preferably substantially free of zinc, silicon, ethereal solvents and aluminum complexes. Further, the present invention provides trialkylantimony compounds substantially free of ethereal solvents. Also provided by the present invention are trialkylbismuth compounds substantially free of ethereal solvents.
The trialkyl Group VA compounds are particularly suitable for use as precursors in CVD, and particularly MOCVD and metalorganic vapor phase epitaxy (xe2x80x9cMOVPExe2x80x9d). The present trialkylstibine compounds are useful for depositing antimony films, the trialkylarsine compounds are useful for depositing arsenic films and the trialkylbismuth compounds are useful for depositing bismuth films. Such films are useful in the manufacture of electronic devices, such as integrated circuits, and optoelectronic devices. For example, trialkylstibine compounds are particularly useful in the production of antimony alloys suitable for use in fiber optic applications, particularly in the 1.3 and 1.55-micron regions. Antimony and antimony alloys are also useful in the 3 to 5 micron region for chemical sensors for infrared countermeasures, communications based on non-silicon dioxide fibers and thermophotovoltaic (xe2x80x9cTPVxe2x80x9d) devices, and in the 8 to 12 micron region for night-vision devices and infrared imaging, and cryogenically cooled, high-mobility electronic devices for high speed.
Films of Group VA metals are typically deposited by first placing the desired trialkyl Group VA metal compound, i.e. source compound or precursor compound, in a bubbler having an outlet connected to a deposition chamber. A wide variety of bubblers may be used, depending upon the particular deposition apparatus used. The source compound is maintained in the bubbler as a liquid or solid. Solid source compounds are typically vaporized or sublimed prior to transportation to the deposition chamber. The source compound is typically transported to the deposition chamber by passing a carrier gas through the bubbler. Suitable carrier gasses include nitrogen, hydrogen, and mixtures thereof. In general, the carrier gas is introduced below the surface of the source compound, and bubbles up through the source compound to the headspace above it, entraining or carrying vapor of the source compound in the carrier gas. The entrained or carried vapor then passes into the deposition chamber.
The deposition chamber is typically a heated vessel within which is disposed at least one, and possibly many, substrates. The deposition chamber has an outlet, which is typically connected to a vacuum pump in order to draw by-products out of the chamber and to provide a reduced pressure where that is appropriate. MOCVD can be conducted at atmospheric or reduced pressure. The deposition chamber is maintained at a temperature sufficiently high to induce decomposition of the source compound. The typical deposition chamber temperature is from about 300xc2x0 to about 1000xc2x0 C., the exact temperature selected being optimized to provide efficient deposition. Optionally, the temperature in the deposition chamber as a whole can be reduced if the substrate is maintained at an elevated temperature, or if other energy such as radio frequency (xe2x80x9cRFxe2x80x9d) energy is generated by an RF source.
Suitable substrates for deposition, in the case of electronic device manufacture, may be silicon, gallium arsenide, indium phosphide, and the like. Such substrates are particularly useful in the manufacture of integrated circuits.
Deposition is continued for as long as desired to produce a film having the desired properties. Typically, the film thickness will be from several hundred to several thousand angstroms or more when deposition is stopped.
Thus, the present invention provides a method for depositing a film of a Group VA metal on a substrate including the steps of: a) conveying a Group VA metal source compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the Group VA metal source compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the Group VA metal compound is prepared by the method including the step of reacting a Group VA metal trihalide with a Group IIIA compound of the formula RnM1X3xe2x88x92n in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C1-C6)alkyl; M1 is a Group IIIA metal; X is halogen and n is an integer from 1-3. In an alternate embodiment, the present invention provides a method for depositing a film of a Group VA metal on a substrate including the steps of depositing a film of a Group VA metal on a substrate including the steps of: a) conveying a trimethyl Group VA metal compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the trimethyl Group VA metal compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the trimethyl Group VA metal compound is substantially free of ethereal solvents and aluminum complexes. In still another embodiment, the present invention provides a method for depositing a film of a Group VA metal on a substrate including the steps of depositing a film of a Group VA metal on a substrate including the steps of: a) conveying a trialkyl Group VA metal compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the trialkyl Group VA metal compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the trialkyl Group VA metal compound is substantially free of ethereal solvents and aluminum complexes, wherein the Group VA metal compound is selected from trialkylstibine, trialkylarsine and trialkylbismuth.
The present invention further provides a method for manufacturing an electronic device including the step of depositing a film of a Group VA metal on an electronic device substrate including the steps of: a) conveying a Group VA metal source compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the Group VA metal source compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the Group VA metal source compound is prepared by the method including the step of reacting a Group VA metal trihalide with a Group IIIA compound of the formula RnM1X3xe2x88x92n in the presence of a tertiary amine in an organic solvent that is free of oxygen substitution, wherein each R is independently selected from (C1-C6)alkyl; M1 is a Group IIIA metal; X is halogen and n is an integer from 1-3. In another embodiment, the present invention provides a method for manufacturing an electronic device including the step of depositing a film of a Group VA metal on an electronic device substrate including the steps of: a) conveying a trimethyl Group VA metal compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the trimethyl Group VA metal compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the trimethyl Group VA metal compound is substantially free of ethereal solvents and aluminum complexes. In a further embodiment, the present invention provides a method for manufacturing an electronic device including the step of depositing a film of a Group VA metal on an electronic device substrate including the steps of: a) conveying a trialkyl Group VA metal compound in the gaseous phase to a deposition chamber containing the substrate; b) decomposing the trialkyl Group VA metal compound in the deposition chamber; and c) depositing a film of the Group VA metal on the substrate; wherein the trialkyl Group VA metal compound is substantially free of ethereal solvents and aluminum complexes, wherein the Group VA metal compound is selected from trialkylstibine, trialkylarsine and trialkylbismuth.
The following examples are presented to illustrate further various aspects of the present invention, but are not intended to limit the scope of the invention in any aspect.